Catheter force control device

ABSTRACT

A catheter force control system including: a hand-held catheter force control device including: a base sized to be hand-held; a cover reversibly fastened to the base in a closed position; a sheath clamp coupled to the base, the sheath clamp capturing a sheath handle to immobilize the sheath handle relative to the base, the sheath clamp is an aperture formed in corresponding abutting edges of the cover and the base, the aperture being formed when the cover and the base are in the closed position; a catheter clamp capturing a catheter, a remote end of the catheter configured to deliver an ablation therapy; the catheter clamp aligned to be substantially co-axial with the sheath clamp; and a linear actuator effecting linear motion of the catheter clamp relative to the sheath clamp; a force sensor located at the remote end of the catheter, the remote end configured for contact with a target tissue, the force sensor detecting real-time contact force data; a controller for receiving the real-time contact force data and for generating and communicating a control signal to the linear actuator to minimize a difference between the real-time contact force data and a preset desired contact force during ablation therapy delivery to the target tissue, the control signal adjusting a position of the linear actuator to compensate for a disturbance of the remote end contact with the target tissue.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/074,753, filed Aug. 1, 2018, which is the U.S. National Phase ofInternational Application No. PCT/CA2017/050119, filed Feb. 2, 2017,designating the U.S. and published in English as WO 2017/132768 A1 onAug. 10, 2017 which claims the benefit of U.S. Provisional PatentApplication No. 62/290,243 filed Feb. 2, 2016. Any and all applicationsfor which a foreign or domestic priority claim is identified here or inthe Application Data Sheet as filed with the present application arehereby incorporated by reference under 37 CFR 1.57.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to catheterized medical procedures, andmore particularly to automated control of catheter contact-force with atarget tissue.

Description of the Related Art

The use of catheters as a medical intervention tool continues to grow inpopularity. For example, many cardiac and vascular surgical proceduresbenefit from catheterization, as surgical procedures can involve largeincisions including cutting of bone and surrounding soft tissue.Recovery time for patients can often be reduced by replacing an invasivesurgical procedure with a catheter procedure.

Percutaneous radiofrequency (RF) catheter ablation is an example of acatheter based procedure that is becoming the standard of care for avariety of cardiac arrhythmias. Cardiac interventionalists introduceablation catheters into the heart and manipulate them until the distaltip contacts the targeted myocardium. Once reached, RF power isdelivered to form ablation lesions that interrupt the electricalpathways responsible for the arrhythmia. For successful treatment it isimportant that these lesions are transmural, as superficial lesionsleave areas of healthy myocardium that may result in conductionrecurrence and ablation failure. For successful treatment the contactforce of the catheter tip onto the tissue needs to be held within adesired range of contact force. Due to motion of the target tissue, themyocardial wall, interventionalists that manually control thecatheter—typically, by observing real time contact force data providedby a catheter type sensor—are incapable of maintaining the desiredcontact force range for a necessary time period.

Manual operation of a catheter presents risk associated withinsufficient contact force or excessive contact force compared to thedesired range. Insufficient contact force presents a risk of anineffective ablation lesion with patients requiring repeat treatments. Aprocedure delivered with excessive contact force presents a risk of deeptissue overheating, which may result in “steam pop”, perforation andinjury outside the heart, including esophageal, pulmonary and phrenicnerve damage.

These potential risks of injury associated with excessive contact forceoften inhibit interventionalists and cause them to deliver the ablationlesion tentatively, erring towards a lower level contact force.

Accordingly, there is a continuing need for automated control ofcatheter contact-force with a target tissue.

SUMMARY OF THE INVENTION

In an aspect there is provided a hand-held catheter force control devicecomprising:

a linear actuator;

a clamp for connecting a catheter to the linear actuator;

the linear actuator controlling contact-force between the catheter and atarget tissue.

In another aspect there is provided a hand-held catheter force controldevice comprising:

an elongate base sized to be hand-held, the base defining a longitudinalaxis between first and second opposing longitudinal ends;

a linear actuator mounted to the base to provide linear motionsubstantially parallel to the longitudinal axis of the base;

a sheath clamp coupled to the base, the sheath clamp sized to fixedlycapture a sheath handle;

a catheter clamp coupled to the linear actuator, the catheter clampsized to fixedly capture a catheter; and

the catheter clamp aligned to be substantially co-axial with the sheathclamp.

In further aspects, systems and methods incorporating the cathetercontact-force control device are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a CFC device 10 having a catheter clamp in an open positionin (A) an isometric view and (B) an isometric wireframe view;

FIG. 2 shows the CFC device 10 having a catheter clamp in a closedposition in (A) an isometric view and (B) an isometric wireframe view;

FIG. 3 shows (A) an isometric view of the CFC device 10 with the housingin a closed position, (B) an axial cross-section view, (C) a lateralcross-section view, and (D) an exploded back-end elevational view;

FIG. 4 shows a flow diagram for a system incorporating the CFC device 10in (A) a first variant, (B) a second variant and (C) a third variant;

FIG. 5 shows a flow diagram for a modification of the system shown inFIG. 4A;

FIG. 6 shows a flow diagram for a fourth variant of a systemincorporating a CFC device;

FIG. 7 shows a schematic view of a linear motion phantom with a catheterand sheath loaded, used to evaluate the CFC device;

FIG. 8 shows a schematic view of the CFC device, sheath and cathetermounted with the linear motion phantom;

FIG. 9 shows two representative patient contact force (CF) profiles ((a)and (c)) and the corresponding CF profiles ((b) and (d), respectively)imposed on a fixed catheter tip by the linear motion phantom, executingthe same patient profile;

FIG. 10 shows a step response of the CFC device for a reference value of25 g, with mean and standard deviation plotted at each time point;

FIG. 11 shows histograms (a)-(c) of the distribution of manual andCFC-controlled CF for three unique motion profiles (16,15, and 9 frompanel(d), respectively), and grey-scale representations of 16 manual (d)and 16 corresponding CFC-controlled (e) interventions (motion profilesin FIG. 9 (b) and (d) are profile #13 and #3, respectively in panel(d));

FIG. 12 shows (a) CF profile, while the CFC was disabled; (b) thegenerated CF profile while the CFC was engaged to deliver 15 g (bottomplot), 25 g (middle plot) and 40 g (top plot); and histogram (c) andgrey-scale representation (d) illustrating the CF distribution betweenmanual and CFC intervention at various desired CF levels (the motionprofile corresponds to profile #1 from FIG. 8(d));

FIG. 13 shows CF profiles for interval 0-20 s (the catheter in contactwith the phantom while the CFC was disabled), interval 20-39.5 s (theCFC engaged to deliver 500 gs at 25 g) and interval 39.5-45 s (the tipof the catheter retracted into the sheath once the desired FTI (dashedline) had been reached), the motion profile corresponding to profile #15from FIG. 8(d).

FIG. 14 shows an isometric view of a variant of the CFC device shown inFIG. 1 with the cover in (A) an open position and (B) a closed position.

FIG. 15 (A) shows a first schematic representation of a controlalgorithm for controlling the CFC device. (B) shows a second schematicrepresentation of a control algorithm for controlling the CFC device.(C) shows a third schematic representation of a control algorithm forcontrolling the CFC device. (D) shows a fourth schematic representationof a control algorithm for controlling the CFC device.

FIG. 16 (A) shows a first CF profile in a simulation using a controlalgorithm shown in FIG. 15, reflecting the difference between PID andSmith predictor (SP). (B) shows a second CF profile in a simulationusing a control algorithm shown in FIG. 15, i.e., a simulation thatshows a comparison between SP (as shown in FIG. 15B) and SP with acardiac disturbance modifier (SP with θm; as shown in FIG. 15C). (C)shows a third CF profile in a simulation using a control algorithm shownin FIG. 15, i.e., a simulation that shows a comparison between SP (asshown in FIG. 15B) and SP with a respiratory disturbance modifier (SPwith F(s); as shown in FIG. 15D).

FIG. 17 (A) shows a CF profile recorded during pig experiments using theCFC device to control catheter contact force at a target location in apig heart, i.e., results from an experiment performed in the left atriumof a pig. (B) a recorded CF profile from another experiment in the rightatrium of the pig heart. (C) A reduction of cardiac disturbances, butlittle to no reduction in respiratory motion disturbances (experimentperformed in the left atrium of the pig). (D) Results from anotherexperiment in a pig—the right atrial septum is dominated by respiratorymotion while cardiac motion is minimal.

FIG. 18 Simulation CF profiles demonstrating effect of deadtime on a PIDcontrol algorithm. (A) shows several plots that may be compared for astability analysis (B) shows several plots that may be compared toanalyze disturbance rejection.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings, various views of a catheter force controller(CFC) device 10 are shown in FIGS. 1 to 3.

FIGS. 1 and 2 both show isometric views with (A) a housing 12illustrated as a solid object hiding a view of interior components and(B) the housing 12 illustrated in wireframe to visualize interiorcomponents. FIG. 1 shows the CFC device 10 disengaged from a catheter 30while FIG. 2 shows the CFC device 10 engaged to the catheter 30. FIG. 3Ais also an isometric view of the CFC device 10, but differs from FIGS. 1and 2 in that a cover 16 of the housing 12 is in a closed position. FIG.3B shows an axial cross-section view taken along line 3B-3B. FIG. 3Cshows a lateral cross-section view taken along line 3C-3C. FIG. 3D showsan exploded back-end elevational view.

The housing 12 of the CFC device 10 comprises a base 14 and a cover 16.The base 14 and cover 16 are substantially symmetrical. Both areelongate, rigid, trough-shaped boxes defining an interior chamber havingsubstantially equal longitudinal and lateral dimensions sized to beconveniently held by one hand. The base 14 defines an open top and thecover 16 defines a corresponding open bottom that are aligned to eachother for open communication between their respective interior chamberswhen the base 14 and cover 16 are placed in a closed position. The base14 is pivotably coupled to cover 16 by hinge 18 with each arm of thehinge 18 joining a corresponding edge contouring the open top of thebase 14 and the open bottom of the cover 16, so that the open top andbottom are aligned when the base 14 and the cover 16 are in the closedposition. First latch 20 and second latch 22 (shown in FIG. 3A) areplaced on an opposing edge to hinge 18 to reversibly fasten the base 14and cover 16 in a closed position.

The housing 12 defines several apertures for receiving structuralcomponents of a catheter-sheath combination. Each of the apertures iscommunicative with the interior chambers of the base 14 and cover 16.Each of the apertures is formed when the base 14 and cover 16 are in aclosed position with a part of the aperture defined in the perimetercontouring the open top of base 14 and the remainder of each aperturedefined in a corresponding location in the perimeter contouring the openbottom of the cover 16. A first aperture 24, formed by alignment ofmated semi-circular cutouts defined at corresponding first ends of thebase 14 and cover 16, is sized to clamp sheath handle 26 so that sheathhandle is fixed to housing 12 and remains stationary relative to thehousing 12 when the base 14 and cover 16 are in a closed position. Asecond aperture 28, formed by alignment of mated rectangular cutoutsdefined at corresponding second ends of the base 14 and cover 16, issized to allow free sliding passage of catheter 30 so that catheter 30can move relative to housing 12 and sheath handle 26 when the base 14and cover 16 are in a closed position. The first and second aperturesare defined at first and second ends of the housing 12 to be inopposition across the longitudinal dimension of the housing 12 and to besubstantially co-axial so that the catheter 30 can be supported linearlyas it spans the longitudinal dimension of base 14 from the firstaperture 24 to the second aperture 28. A third aperture 32, formed byalignment of mated semi-circular cutouts defined at a corresponding sidelocation proximal to the first ends of the base 14 and cover 16 is sizedto receive side port 34, which extends radially outward from sheathhandle 26, so that side port 34 can maintain a connection with waterline 36 when the base 14 and cover 16 are in a closed position. Waterline 36 supplies a suitable liquid, such as an isotonic saline solution,to reduce friction between the sheath and catheter and provideirrigation during RF application, for example to provide cooling and/ordrug delivery. The axis of third aperture 32 is aligned substantiallyperpendicular to the axis of first aperture 24 to accommodate the radialorientation of side port 34. The second aperture may be interchangeablyreferred to as a guide aperture. The third aperture may beinterchangeably referred to as a side port aperture.

The sheath handle 26 comprises a tubular body 38 with an entry valve forinsertion of a catheter 30. A first end of the entry valve supports ahemostatic seal 40 defining an insertion point sized to receive catheter30 while a second end of the entry valve forms a neck 42 integrallyconnected with a terminal shoulder of the tubular body 38. Neck 42 islocated in between hemostatic seal 40 and tubular body 38 and neck 42has a smaller diameter than both hemostatic seal 40 and tubular body 38.Therefore, sizing the first aperture 24 to capture or clamp neck 42 andbuttressing the first end of the housing 12 against the terminalshoulder of the tubular body 38 that joins neck 42 effectively preventsmotion of the sheath handle when base 14 and cover 16 are in a closedposition.

A linear actuator 44 is mounted within the interior chamber of base 14.The linear actuator 44 is a sled and slide track mechanism having asingle Degree of Freedom providing back-and-forth linear motion. Thesled is a coil assembly 46 and the slide track is a magnetic rod 48. Thecoil assembly 46 contained within a suitable housing with bushings ismounted on the magnetic rod 48 which in turn is mounted to base 14. Afirst limit switch 60 is mounted to the first end of base 14 and asecond limit switch 62 is mounted to the second end of base 14. Firstand second limit switches are used for a homing protocol and may also beused as over-travel or end-of-range kill switches during operation ofthe CFC device 10.

During operation, the linear actuator 44 is communicative with acontroller. A connector port (not shown), for receiving control signalsfrom a controller/driver circuit with communication to the linearactuator, is mounted within base 14 with the connector port (not shown)accessible from an exterior surface of the base 14 to connect acorresponding connector cable (not shown) from the controller/drivercircuit.

A catheter clamp 50 is mounted to the housing of the coil assembly 46.The catheter clamp 50 comprises an elongate bottom plate 52 and amatching equally dimensioned top plate 54. Bottom plate 52 is mounted tothe housing of coil assembly 46 and top plate 54 is reversibly fastenedto bottom plate 52 with bolts 58. Bolts 58 extend through bores formedin top plate 54 and are rotated to threadingly engage blind threadedbores formed in bottom plate 52. Top plate 54 and bottom plate 52 may bepivotably coupled along a common edge to reduce the number of boltsneeded to reversibly fasten the catheter clamp 50 in a closed position.The top plate 54 provides a contact surface that abuts a correspondingcontact surface of the bottom plate. A partial-pipe channel, typically ahalf-pipe channel, is formed co-extensively within each of the contactsurfaces. A full-pipe channel 56 is formed when the top plate 54 isreversibly fastened to the bottom plate 52. Thus, the full-pipe channel56 is formed when the catheter clamp 50 is in a closed position with apart of the channel defined by the contact surface of the bottom plate52 and the remainder of the channel defined by the contact surface ofthe top plate 54.

The full-pipe channel 56 is sized to frictionally engage catheter 30 andis substantially co-axial with first aperture 24 and second aperture 28so that capture of catheter 30 within full-pipe channel 56 maintains asubstantially linear path for catheter 30 from first aperture 24 throughthe interior chamber of the housing 12 to the second aperture 28.Frictional engagement between the catheter 30 and full-pipe channel 56may include a lining of rubber or other suitable material with a highfriction coefficient on part or all of the length of the full-pipechannel 56. During operation, sheath handle 26 is clamped by firstaperture 24 remaining fixed to housing 12, while catheter clamp 50mounted on linear actuator 44 captures catheter 30 and thereby effects alinear motion of the catheter 30 relative to sheath handle 26.

FIG. 4A shows a flow diagram of a cycle of a CFC system 70 incorporatingthe CFC device 10. Once a sheath 39 and catheter 30 are manually orrobotically maneuvered so that a tip or remote end of the catheter 30 isat a target location the CFC device 10 is coupled to the catheter 30 andsheath handle 26 as shown in FIGS. 1 to 3 with both catheter clamp 50and housing 12 in a closed position. The CFC system 70, and morespecifically a hybrid proportional-derivative-integral (PID) controller76 generates a pulse-width modulated (PWM) control signal referenced toa preset desired contact force 72. The PWM control signal iscommunicated to a velocity proportional-integral (PI) controller 78 thatgenerates a control signal to control velocity of the linear actuator 44based on the input PWM control signal. The control signal generated byPI controller 78 is communicated to driver circuitry 80 which in turnoutputs the control signal with supply voltage and current that matchesthe requirements of linear actuator 44. Linear motion of linear actuator82/44 is tracked using encoders and the position 86 of the linearactuator is communicated back to PI controller 78 to calculate change ofposition. Motion of the linear actuator 82/44 imparts motion to catheter30 resulting in linear motion at the catheter tip 84. As the cathetertip touches the tissue a force sensor 90 measures the contact forcebetween the catheter tip and target tissue. Disturbances 88 cause theforce measured by contact force sensor 90 to change. Disturbances 88include cardiorespiratory motion 88A, catheter instability 88B, andpatient motion 88C. Contact force 92 is communicated in real-time to thehybrid PID controller 76 which executes a comparison 74 of the real-timecontact force data 92 to the preset desired contact force 72 and beginsa new round of the cycle by generating a new PWM control signal tominimize the difference between the real-time force data 92 and thepreset desired contact force 72.

FIG. 4B illustrates a variant of the cycle shown in FIG. 4A where theposition 86 of linear actuator 82/44 is directly fed back to contactforce controller 75

FIG. 4C illustrates a variant of the cycle shown in FIG. 4B whereadditional input parameters 96 are fed to contact force controller 77 toprovide additional arguments that influence the control signal fed todriver circuitry 80.

FIG. 5 shows an implementation of the cycle shown in FIG. 4A with theaddition of a foot pedal 108 to control a start and stop of the cycleand an optional catheter robotic navigation system 105. Theinterventionalist can manipulate a catheter tip to a targeted locationguided by a catheter mapping system represented in a graphic userinterface installed and operating on a local computer 102. The sheath 39may be manipulated manually by sheath handle 26 to position catheter 30to the target location. Once at the target location the CFC device 10can be coupled to the catheter 30 and sheath handle 26. Optionally, arobotic catheter navigation system 105 may advance catheter 30 throughsheath 39 to the target location, by relaying position commands 106 toCFC 111. While the force controller is not engaged 110, CFC 111 permitsmanual robotic catheter operation 112. To engage 110 the CFC system 111the foot pedal 108 is pressed resulting in catheter control forcecontroller 114 generating a control signal to minimize the differencebetween real-time contact force and preset desired contact force 104.The contact force controller 114 can be any of controllers 75, 76, or77. Input parameters 104, such as catheter incident angle, ECG, tissuetemperature or tissue impendence, may also be an input for generation ofthe control signal. The control signal is outputted to the motor drivercircuitry 116 which communicates the control signal to the linearactuator 118 with suitable supply voltage and current that matches theoperational requirements of the linear actuator 118. Linear motion ofthe linear actuator 118 effects a corresponding linear motion of thecatheter 120 providing a contact between the catheter and the targettissue and providing a new contact force data point detected by forcesensor 122. Disturbances 121 may vary contact force. The new contactforce data point 125 is communicated to local computer 102 which in turncommunicates the data point to controller 114 to start the cycle overagain. If the foot pedal is disengaged, the linear actuator and thecatheter are retracted to a reference position. A serial communicationprotocol enables communication between the controller and a localcomputer. Optionally, with the foot pedal 108 disengaged theinterventionalist may robotically move the catheter to a desiredposition 106 using a robotic catheter navigation system 105.

FIG. 6 shows a variant of the CFC system engaged to deliver a desiredcontact force 200 to the target tissue until a desired force timeintegral (FTI) 202 or other lesion size metric is reached. The cathetercontact force controller 204 engages catheter motion 206 through thesheath 39 onto the target tissue. The new contact force data point 210is communicated to CFC system 211. CFC system 211 calculates cumulativeFTI 212 and compares 214 with desired FTI 202. If desired FTI 202 is notreached, the contact force controller 204 generates a new control signaland starts the cycle over again. When the desired force time interval202 is reached in comparison 214 the catheter 30 is withdrawn back intothe sheath 39 to a reference position. The contact force controller 204can be any of controllers 75, 76, or 77.

The CFC device provides several advantages in a clinical setting. Forexample, the CFC device is a convenient hand-held tool that provides theability to deliver ablation lesions in an optimal and controlled manner.Currently, there are no commercial devices that enable contact forcecontrol of the catheter tip. As another example, the CFC device can bereadily retrofit with existing commercially available catheter systems.The CFC device can be an additional tool to standard catheterizationprocedures using off-the-shelf catheters and sheaths across multiplecatheter manufactures. This feature of the device is advantageous asthere is no need for specialized proprietary instruments and does notrequire the redesign of infrastructure of the operating room, which isoften the case for catheter robotic systems. As yet another example, theCFC is completely compatible as an add-on device with manualintervention; it can be added after the interventionalist has insertedthe sheath and catheter into the vascular system, can be removed at anytime and subsequently repositioned without compromising the sterility ofthe sheath and catheter.

The successful use of the CFC device has been demonstratedexperimentally to show a desired contact-force control between acatheter tip and a target surface. Illustrative experimentaldemonstrations of the CFC device are now described.

Percutaneous radiofrequency (RF) catheter ablation is becoming thestandard of care for a variety of cardiac arrhythmias. Cardiacinterventionalists introduce ablation catheters into the heart andmanipulate them until the distal tip contacts the targeted myocardium.Once reached, RF power is delivered to form ablation lesions thatinterrupt the electrical pathways responsible for the arrhythmia. Forsuccessful treatment it is important that these lesions are transmural,as superficial lesions leave areas of healthy myocardium that may resultin conduction recurrence and ablation failure.

Catheter-tip-to-tissue contact force (CF) has been shown to be anindicator for assessing lesion development, and CF guidelines have beenestablished to label a delivered lesion as effective. Additional studieshave shown that monitoring both the duration of the delivery and CF at aspecific RF power can predict lesion volume. Conventionally described asa Force-Time Integral (FTI), the model may be used as a prospectivequantitative tool to determine lesion volume under defined parameters.Unfortunately, this model is dependent on catheter stability and whileused in the clinic as a guide, it has not been used as a quantitativemetric that can predict lesion volume or transmurality. Finally, lesionsdelivered with excessive CF present a risk of deep tissue overheating,which may result in “steam pop”, perforation and injury outside theheart, including esophageal, pulmonary and phrenic nerve damage. Thesepotential risks often inhibit the interventionalist and cause them todeliver the lesion tentatively, with a lower level of CF to lessen therisk of injury. Clinically, CF information is often used as a guide toensure catheter tip contact and confine the CF within acceptable ranges,but is ultimately limited by tissue motion, as seen in the CF profile inthe lower right-hand corner of FIG. 1.

While ideally the CF should be regulated within a prescribed range,interventionalists cannot respond fast enough to compensate for cardiacand respiratory motion. Approaches to minimize myocardial motion duringablation, have been proposed, including high-frequency-jet ventilation.None have successfully provided a motionless environment in allpatients.

Commercial force-sensing ablation catheters enable the interventionalistto simultaneously monitor the CF in real-time while delivering thelesion. Often these catheters are used together with steerable sheaths,whose added level of versatility and stability has increased clinicalsuccess. The interventionalist typically manipulates the steerablesheath until the catheter is pointing at the target region, and thenadvances the catheter forward through the sheath until the desired levelof CF is imparted onto the tissue.

Hand-Held Device. The hand-held CFC device is mechanically clamped tothe distal end of the sheath handle (i.e. at the hemostatic seal andinsertion point of the catheter). A catheter-locking adapter rigidlyclamps the catheter shaft onto a precision linear actuator (LM2070-040,MICROMO, Clearwater, USA) traveling along a 12 mm diameter 134 mm longprecision magnetic shaft. Movement of the actuator directly translatesto movement of the catheter through the sheath. The adapter and actuatorare mounted within an enclosure, which is designed to securely lock ontothe sheath handle, while keeping the catheter concentrically mountedwithin the hemostatic seal. A set of hinges and latches enables easyclamping and removal of the CFC. Both the adapter and enclosure werefabricated in polypropylene using additive manufacturing (Objet3D Pro,Stratasys Ltd., Rehovot, Israel).

Hybrid Control System. A hybrid control system maintains a prescribed CFbetween the tip of the catheter and a moving target. Common closed-loopproportional-integral-derivative (PID) control algorithms are based onminimizing the error between the desired and actual inputs, and havebeen shown to be a viable solution in robotic catheter control systems.The CFC uses a hybrid PID controller, a slight variation of a standardPID controller, whose control parameters change based on the errorargument. The control signal u(t) is calculated as:

${u(t)} = \left\{ \begin{matrix}{{K_{P_{A}}{e(t)}} + {K_{I_{A}}{\int_{0}^{t}{{e(\tau)}\ d\;\tau}}} + {K_{D_{A}}\frac{d}{dt}{e(t)}}} & {{e(t)} > F_{T}} \\{{K_{P_{C}}{e(t)}} + {K_{I_{C}}{\int_{0}^{t}{{e(\tau)}\ d\;\tau}}} + {K_{D_{C}}\frac{d}{dt}{e(t)}}} & {0 < {e(t)} \leq F_{T}}\end{matrix} \right.$where the error e(t) is the difference between the desired and currentcontact forces, F_(D) and F_(C)(t) respectively. The control parametersK_(P), K_(I) and K_(D) generate a different control signal depending onthe error measured in real time. If the error is larger than apredefined CF threshold, F_(T), the control system is in an “aggressive”state indicated by K_(PA), K_(IA), K_(LA). When the error is lower thanF_(T) the control system operates in a “conservative” state indicated byK_(PC), K_(IC), K_(DC). The CF threshold was empirically assigned to be5 g—a level that was observed to retain steady-state accuracy. Tuning ofthe aggressive control parameters was achieved using the Tyrues-Luybentuning method (B. D. Tyreus, and W. L. Luyben, “Tuning PI controllersfor integrator/dead time processes,” Industrial & Engineering ChemistryResearch, vol. 31, no. 11, pp. 2625-2628, 1992). The conservativecontrol parameters were manually tuned for a desired steady-stateresponse; in the current implementation, the conservative controlparameters were at least a factor of 4 smaller than the aggressive ones.

Electronic Hardware Design. The hybrid control system was implementedwithin an embedded electronic system, enabling real-time control of thelinear actuator. A microcontroller development platform based on a AtmelSAM3X8E 84 MHz 32-bit ARM architecture (Due, Arduino LLC, Ivrea, Italy)generates a pulse-width modulated (PWM) control signal, based on themeasured and desired contact force, which acts as input to the linearactuator controller and driver circuitry (MCLM-3003, MICROMO,Clearwater, USA). This daughter board is programmed with a nativevelocity proportional-integral (PI) controller that controls the speedof the motor based on the input PWM signal. Tuning of the PI controllerwas performed using the manufacturer's tuning software, before tuningthe hybrid PID system. The update rate of the hybrid PID system was setto 1 kHz, which was the maximum rate of the linear actuator controller.

Linear Motion Phantom. To evaluate the CFC's ability to regulate CF on amoving target in vitro, a custom built linear motion phantom wasdeveloped (FIG. 7). The motion phantom was built to provide sinusoidaland physiologic motion profiles. A gear motor with a Hall effect encoder(37D Gearmotor, Pololu Electronics, Las Vegas, NV, USA) drives a leadscrew mechanism providing linear motion to a carriage. A second PIDcontrol system within an embedded electronic system controls the motionstage: the circuit board assembly includes a microcontroller developmentplatform (Due, Arduino LLC, Ivrea, Italy) and a DC motor driver daughterboard (VNH5019 Driver Shield, Pololu Electronics, Las Vegas, Nev., USA).A strain gauge capable of detecting force with 200-milligram resolution(S100, Strain Measurement Devices, Wallingford, Conn., USA), coupled toa linear amplifier (CSG110, FUTEK Inc., Irvine, Calif., USA), is mountedon the carriage and used to measure the CF of the tip of the catheter. Apiece of silicone (Dragon Skin 30, Smooth-On Inc., Macungie, Pa., USA)is positioned between the strain gauge and the tip of the catheter tomimic soft tissue compliance. A setscrew fixes the sheath firmly inplace without hindering movement of the catheter housed within thesheath. Linear calibration, according to Hooke's law, was firstperformed to determine the relationship between the displacement of thetissue and the force measured by the strain gauge. The phantom wasprogrammed to execute arbitrary sinusoidal and sine-sweep motionprofiles and to replicate physiological motion. Contact force profileswere recorded by force-sensing ablation catheters during typicalablation procedures, similar to the profile illustrated in FIG. 1. Theseprofiles, containing both high-frequency low-amplitude cardiac andlow-frequency high-amplitude respiratory motion, were programmed intothe motion phantom as position trajectories, using the linearcalibration parameters. The signal from the strain gauge, measured inreal time, was used as the CF feedback signal of the CFC control systemand represents a surrogate of the CF signal that would be provided by acommercial force-sensing catheter.

Linear Motion Phantom Evaluation. The linear motion phantom was firstevaluated to ensure that the executed motion profiles mimic thephysiological motion that results in contact force profiles similar tothose measured clinically. The catheter was held fixed while the linearmotion phantom imposed 16 different patient-specific motion profiles.The sheath was locked in place for half of the experiments. Thereal-time CF measurements provided by the strain gauge were recorded andcompared to the corresponding CF profiles. No attempt was made toperfectly match the executed CF profiles to the corresponding patientprofiles and the measured CF profiles were only inspected visually,ensuring the range of amplitudes and frequencies were within thephysiologic range.

Catheter Force Controller Evaluation. Experiments were performed toevaluate the overall accuracy and dynamic performance of the CFC. Forthese experiments, the CFC was attached to the rear end of a commonlyused steerable sheath (8F Agilis NxT, St. Jude Medical, Saint Paul,Minn., USA) and CF sensing ablation catheter (7.5F SmartTouch, BiosenseWebster Ltd., Diamond Bar, Calif., USA) combination. Water wasintroduced via the sheath's side port to mimic the clinical setting andreduce the friction between the sheath and catheter. The sheath andcatheter were inserted into the linear motion phantom as illustrated inFIG. 8.

1) Step Response: The response of the CFC control system to a step input(of 25 g) was first evaluated. The step response was then measuredduring 25 repeats and the rise time, overshoot, and peak level werecharacterized. During these experiments, the linear motion phantom waskept fixed.

2) Safety: The CFC was tested for response to excessive, fast and suddenmotions that may result in tissue perforation. The linear motion phantomwas programmed to impose a bidirectional continuous sine sweep motionprofile, sweeping from 0.1 Hz to 2.5 Hz with amplitude of 70 gpeak-to-peak. This unlikely clinical scenario was selected followingFourier analysis of over 40 patient-specific CF profiles and determiningthat the maximum frequency component observed was 2.5 Hz. While thephantom executed the prescribed motion, the CFC was engaged andattempted to regulate the CF to a desired reference of 25 g. The maximumerror between the desired and actual contact force was measured. Thisexperiment was repeated 10 times.

3) Patient-Specific Dynamic Response: To evaluate the overallperformance of the CFC versus manual intervention, the linear motionphantom was programed to execute 16 different patient motion profiles.Prior to any evaluation of the CFC, a control experiment was performedwhereby the phantom replicated each profile with the CFC's disabled.This is representative of manual intervention, where theinterventionalist contacts the catheter to moving myocardial tissue andholds the catheter still to deliver a lesion. The experiment was thenrepeated with the CFC programmed to deliver 15 g, 25 g, and 40 g for theduration of the motion profile. Statistical analysis of the regulated CFprofiles was performed to calculate mean, confidence interval, androot-mean-squared error (RMSE). Histograms of CF were also plotted forthe “manual” and CFC interventions. Note that for this study we use theterm “manual” to refer to the CF profile representative of CF profilesrecorded during clinical ablation procedures.

4) Force-Time Integral: This experiment was designed to demonstrate thatthe CFC could be used not only to regulate the delivered force, but alsoto deliver lesions with prescribed FTI. The CFC was programmed todeliver a prescribed FTI at a desired CF while the linear motion phantomimposed a patient motion profile. For each FTI/CF combination anexpected duration can be calculated. The CFC was programmed to calculatethe FTI, and automatically retract the tip of the catheter back into thesheath once the desired FTI was reached. The generated CF profile andduration of catheter engagement was recorded and compared with expectedvalues. This experiment was then repeated for various configurations ofFTI and CF, which may be user-defined in a clinical setting. The testedFTI values were 500, 1000, and 1500 gs, where each was repeated with 25g and 40 g of CF. Each configuration was repeated 3 times.

Linear Motion Phantom Results. The linear motion phantom was able toreplicate a range of patient-specific CF profiles. The profiles chosento evaluate the CFC are characteristic of typical cardiorespiratorypatterns depicted in FIG. 9(a) as well as irregular profiles associatedwith patient motion or catheter instability depicted in FIG. 9(c). Thegenerated CF curves, shown in FIG. 9(b, d), visually demonstrate a highlevel of similarity to the corresponding clinically acquired profiles(FIGs. 9a and c ). These results demonstrate that the linear motionphantom is able to replicate cardiorespiratory forces that is typicallyencountered during catheter RF delivery and is appropriate to be used asa phantom for the CFC' s evaluation. Locking the sheath in place did notaffect the results.

CFC—Step Response—Results. The response of the CFC's control system to a25 g step input is shown in FIG. 10. The following step responsecharacteristics were calculated from the measurements: 38±3 ms risetime, 3±2 g overshoot, and peak of 29±2 g; means and standard deviationsof 25 repeats of the step response are reported. The negligibleovershoot and oscillation indicate that the tuning method used todetermine the control parameters has resulted in a desired transient andsteady state response.

CFC—Safety—Results. During the control of a 70 g peak-to-peak sine sweepfrom 0.1 Hz to 2.5 Hz, the maximum difference between the prescribed andmeasured CF was 15±2 g, with all measured CF values being below 42 g.These results demonstrate that the CFC is capable of reacting to suddenchanges of tissue displacement that would otherwise result in largespikes of CF and potentially cause tissue damage.

CFC—Patient-Specific Dynamic Response—Results. The CFC was able tosignificantly transform the CF profile on the catheter tip in comparisonto manual intervention (p<0.001). FIG. 11(a-c) depicts the distributionof measured CF for three motion profiles, representative of CFs measuredduring the delivery of different lesions; histograms are plotted forboth manual and CFC-controlled interventions, with a prescribed CF levelof 25 g. The images in FIG. 11(d, manual) and FIG. 11(e, CFC-controlled)are grey-scale representations of the CF histograms for all 16 motionprofiles; they clearly demonstrate that when the CFC is engaged theprescribed mean force is achieved for all motion profiles. Similarperformance was achieved regardless of the magnitude of the prescribedCF. Illustrated in FIG. 12, are the results for one representativeexperiment where the CFC was programmed to deliver a CF of threeclinically relevant levels—15, 25, and 40 g. Consistently similar forcedistributions, were achieved regardless of the prescribed CF value.Detailed performance metrics—averaged over all tested motionprofiles—are shown in Table I for the three prescribed CF levels.

TABLE I PATIENT MOTION EXPERIMENTS Prescribed CF (g) 15 25 40 5%Percentile 10.1 ± 1.2 19.7 ± 1.2 34.3 ± 1.2 95% Percentile 20.6 ± 1.331.1 ± 1.5 46.9 ± 1.7 Mean 15.3 ± 0.1 25.4 ± 0.1 40.4 ± 0.1 RMSE  3.2 ±0.6  3.4 ± 0.7  3.9 ± 0.8

CFC—Force-Time Integral—Results. For all experiments performed todemonstrate that the CFC could achieve a target FTI, the CFCsuccessfully engaged the catheter with a desired CF until a target FTIwas reached. The results obtained with each configuration of FTI and CFare presented in Table II. A representative experiment is illustrated inFIG. 13. The lesion delivery time was within 480±199 ms of the expectedduration. This is indicative of a regulated CF profile throughout thedelivery, as excessive CF would result in short lesion delivery timesand low CF levels would result in the opposite. With each configurationof desired CF and FTI a similar profile was generated with an expectedand predicable deviation.

TABLE II FORCE-TIME INTEGRAL EXPERIMENTS Desired Expected Measured FTICF Duration FTI CF Duration (gs) (g) (s) (gs) (g) (s) 500 25 20 500 25.7± 3.0 19.49 ± 0.01 40 12.5 500 40.7 ± 3.5 12.29 ± 0.01 1000 25 40 100025.4 ± 3.1 39.36 ± 0.04 40 25 999 40.4 ± 3.4 24.71 ± 0.01 1500 25 601500 25.3 ± 3.0 59.27 ± 0.06 40 37.5 1499 40.4 ± 3.4 36.99 ± 0.22

The CFC is an easy to use tool that regulates the CF imparted bystandard ablation catheters on moving tissue regardless of the type ofmotion imposed. The compact hand-held device is used with commerciallyavailable force-sensing ablation catheters and steerable sheaths, whichare widely used in modern electrophysiology suites. The presented CFCutilizes the same tools and information available to theinterventionalist but grants the ability to regulate CF and FTI.

While contact force measurement (at the tip of an ablation catheter) hasbeen available to electrophysiologists for some time, it has been usedprimarily as a visual guide to determine if adequate contact has beenmade or if there is a risk of tissue perforation. The CFC has beendemonstrated to control the force at the tip of the catheter to within afew grams of a prescribed force level.

The CF profiles, recorded during clinical ablation procedures, used toimpart clinically relevant motion for evaluating the CFC and shown inFIG. 11 demonstrate some of the problems associated with ablationdelivery. For example, profile #16 (FIG. 11(a)) represents a lesionwhere negligible force existed between the catheter tip and the wallduring most of the time RF power was being delivered; when the CFC wasengaged the mean CF was increased to 25 g, as prescribed. Similarly, thescenario depicted in FIG. 11(b) demonstrates large variations in contactforce (manual) due to motion, which is corrected via the use of the CFC,reducing the RMSE (about 25 g) from 15.1 to 5.5 g. Even when a tightdistribution of forces is achieved manually, as in FIG. 11(c), the meanCF may not be at a level sufficiently high for the delivery of atransmural lesion—use of the CFC in this case shifts the distribution ofCF from being centered about 15 g to being centered about 25 g.Consistently narrow, and symmetric, distributions of CF were alsoachieved for different prescribed CF levels (FIG. 12, Table I).

Successful control of CF over the duration of lesion delivery alsoenabled control of FTI. Automatic engagement and retraction of thecatheter for specified FTI at a desired CF has the potential to become afundamental and powerful tool in the electrophysiology suite. While FTIhas been proposed as a useful measure in predicting lesion transmuralityand volume, without a device like the CFC FTI cannot be easily used as ametric clinically or in preclinical studies aimed at optimizing lesiondelivery parameters.

The study evaluating the performance of the CFC under conditions ofrapidly varying motion have also demonstrated that use of the CFCclinically has potential to minimize tissue damage due to excessiveforce. The CFC was able to compensate for changes in CF as fast as 700g/s and maintain CF within 15 g of the prescribed values. These resultsare significant because they indicate that using the CFC, forces able toperforate tissue are not produced.

The CFC is a hand-held device that enables the interventionalist toengage it at any point during a complete ablation procedure, but is freeto perform all other tasks as is done under current clinical practice.The CFC can easily be removed from the catheter/sheath assembly toensure optimal catheter steerability and be re-clamped when a targetlocation has been reached, just prior to RF power delivery. The deviceis versatile and can be used as a stand-alone CF control aid or can beincorporated with catheter robotic navigation systems for furtherimprovements in position and force control.

An illustrative version and several variants of a CFC device and asystem and method incorporating the same have been described abovewithout any intended loss of generality. Further examples ofmodifications and variation are contemplated.

For example, any suitable type of clamp may be used to immobilize asheath handle to the CFC device. Similarly, any suitable type of clampmay be used to fix the catheter to the linear actuator. In one example,the clamp for the catheter provides a reversibly closeable full-pipechannel lined or layered with a gripping material such as rubber or anyother suitable material having a high coefficient of friction.

The sheath clamp may engage any portion of the sheath handle toimmobilize the sheath handle to the CFC device including, for example, aneck, a tubular body or both the neck and the tubular body of the sheathhandle. As shown in FIGS. 1 and 2, first aperture 24 can capture orclamp a neck of a tubular body when the housing 12 is in a closedposition. Similarly, a clamp may be configured to capture the tubularbody 38 of the sheath handle 26. For example, as shown in FIG. 14, afirst jaw 64 may be connected or integrally formed with a longitudinalend of cover 16 while a second jaw 65 may be connected or integrallyformed with a corresponding longitudinal end of base 14. The first jaw64 provides a first mating surface 66 while the second jaw 65 provides asecond mating surface 67. When housing 12 is in a closed position, thefirst mating surface 66 and the second mating surface 67 cooperate toengage radially opposed surfaces of the tubular body. The first andsecond mating surfaces may be texturized with surface features such asteeth, ridges, dimples, and the like to facilitate grip. The first andsecond mating surfaces may be formed of or layered with rubber or othersuitable materials having a coefficient of friction that facilitatesgrip.

Sheath handles may be formed without the hemostatic seal shown, forexample, in FIG. 1. Similarly, sheath handles may be formed without theneck structure shown, for example, in FIG. 1. Therefore, the sheathclamp may comprise first and second jaws 64 and 65 that cooperate tocapture a tubular body of the sheath handle in addition to or instead ofa sheath clamp that captures a neck structure of the sheath handle. Thesheath clamp may incorporate any suitable type of clamp that effectivelyimmobilizes the sheath handle relative to the housing of CFC device.Sheath clamps may not require connection to both the cover and the baseand clamps connected to either the cover or the base may be sufficient.For example, a C-clamp fixed on a post extending from either the base orthe cover may function as a sheath clamp. The post extending from thebase or the cover is oriented parallel to the longitudinal axis of thehousing and the sheath handle, while with the C-clamp is orientedtransverse to the longitudinal axis of the housing and the sheathhandle. With the C-clamp in an open position the sheath handle ispositioned within the open ring defined by ends of the C-clamp, and thena toggled latch that closes and brings the ends of the C-clamp closertogether can be used to tighten the clamp and capture the sheath handle.Similarly, a sheath clamp may comprise an 0-shaped hose ring fixed on apost extending from either the cover or the base with a worm screw drivein threaded communication with the hose ring and operable to reduce orexpand the diameter of the hose ring. Many other types of clamps areconventionally available and may be suitable to be included as a sheathclamp.

The sheath clamp may be substituted with any reversible connector orreversible fastener mechanism that allows the sheath handle to beremovably coupled to the housing of the CFC device and functions toimmobilize the sheath handle relative to the housing during operation ofthe CFC device.

The sheath clamp and the catheter clamp are typically aligned to besubstantially co-axial so that during operation of the CFC device thecatheter is maintained in a substantially co-axial alignment throughoutthe housing of the CFC device. However, deviation from co-axialalignment can be accommodated. Deviation from co-axial alignment willtypically be less than about 30 degrees. Often deviation from co-axialalignment will be less than about 20 degrees. More often deviation fromco-axial alignment will be less than about 10 degrees.

The linear actuator may be any suitable type and need not be limited toa sled and slide track mechanism. For example, the linear actuator maybe a lead screw and lead nut with a rotary stepper or DC motormechanism. In another example, the linear actuator may be apiezoelectric actuator or a voice coil.

The CFC device can accommodate any type of catheter including rigid orflexible catheters, needles or probes.

The CFC device may accommodate various controller types and controlleralgorithms to control contact-force of a catheter tip with a targettissue. For example, proportional-integrative-derivative (PID),proportional-integrative (PI) or proportional (P) algorithms may be usedto control the CFC device depending on parameters of a specificimplementation. Where PID algorithms are overwhelmed by time-delay in asystem, various time-delay compensating algorithms are known that can beincorporated as desired depending on parameters of a specificimplementation. For example, several time-delay compensating algorithmsare described in: Control of Dead-time Processes, By J Normey-Rico, E FCamacho ch. 1 and 5; PID Controllers for Time-Delay Systems, ByGuillermo J. Silva, Aniruddha Datta, Shankar P. ch. 1, 7, and 8;Industrial Digital Control System, By K. Warwick and D. Rees. ch. 5;www.mathworks.com/help/control/examples/control-of-processes-with-long-dead-time-the-smith-predictor.html;Industrial Digital Control System, By K. Warwick and D. Rees. ch. 10.Time-delay compensation can also be achieved by adaptive controlalgorithms as described, for example, in: Industrial Digital ControlSystem, By K. Warwick and D. Rees. ch. 10; and Control of Dead-timeProcesses, By J Normey-Rico, E F Camacho ch. 4. Kalman Filtering canalso be useful for time-delay compensation as described, for example,in: K. S. Walgama, “Control of Processes with Noise and Time Delays”,AIChE, 1989, Vol 35, No. 2. Model Predictive Control (MPC) may also beuseful for time-delay compensation as described, for example, in:Control of Dead-time Processes, By J Normey-Rico, EF Camacho ch. 9.Dahlin controller, which uses an internal model control technique (IMC)may also be useful for time-delay compensation as described, forexample, at:web.stanford.edu/class/archive/ee/ee392m/ee392m.1056/Lecture11_IMC.pdf.Still further control algorithms are available that may benefit controlof a process involving a time-delay or deadtime.

FIG. 15 provides flow diagrams of various illustrative controlleralgorithms that may be used to control the CFC device.

As represented schematically in FIG. 15A,proportional-integrative-derivative (PID) is a control loop negativefeedback mechanism used universally in control applications. PIDcontrollers calculate the error between the desired and measuredcontact-force, e(t), and apply a correction control signal, u(t), whichis sent to the linear actuator of the device. As the linear actuatorresponds and translates the catheter through the sheath, a newcontact-force reading is acquired and the loop repeats. The controller,C(s), is a PID transfer function relating the error and control signalto the motor, and the process, G(s), is a real world system relating thecontrol signal to the motor and the resulting contact-force response.The closed-loop system compensates for output disturbances, includingcontact-force fluctuations caused by cardiorespiratory motion. While PIDcontrollers provide a functional solution in many operatingenvironments, a potential drawback to PID controllers is the sensitivityto time delay or deadtime, θp, in the control loop, which can lead toinstability of control and diminish performance.

Control schemes are known that provide a means of alleviating thedifficulty of controlling processes involving time delays. Such controlschemes including, for example, a Smith Predictor, Gain-Adaptive PID, aKalman filter or other suitable time-delay compensating algorithms maybe incorporated to mitigate the effect of the deadtime in the controlloop. As shown in FIG. 15B, the Smith predictor (SP) includes anordinary feedback loop plus an inner loop that introduces a model of theprocess; the model of the process takes the form of a transfer functionĜ(s), and an estimate of the deadtime, θpm. In this configuration, ifĜ(s)=G(s) and θpm=θp, then the feedback yields an estimate of thedisturbances without deadtime.

The real world process G(s) captures all the dynamics of the CFC deviceand the system used to control it. This includes, for example, theinertia of the motor, the compliance in the catheter, the compliance ofthe tissue, the dynamics of the force sensor, and the like. G(s) is ahidden relationship between the control signal to the motor and theoutput contact-force response. Ĝ(s) is a numerical model being processedon a microcontroller. This model can be developed using any suitablemodeling software including, for example, a MATLAB(mathworks.com/products/matlab) black-box system identification methodusing input-output data.

Although the Smith predictor improves closed-loop performance ininstances where deadtime is a significant concern, output disturbanceswith frequencies above θ_(p) ⁻¹ rad/s will not be reduced. In commercialforce-sensing catheter systems, the amount of deadtime present in thesystem can prevent disturbance rejection of cardiac motion. As shown inFIG. 15C, an improvement to the Smith predictor control system may beintroduced, where, an extra deadtime term θ_(m), is introduced, whichfurther delays the feedback.

The extra delay is calculated as θm=T−θpm, where T is the period of theheartbeat of the patient. For instance, if the deadtime of the system is0.1 seconds and the heartbeat of the patient is 75 BPM (0.8 seconds),then θm equals to 0.7. This calculation assumes that the heartbeat doesnot significantly fluctuate (since the majority of catheter ablationprocedures use pacing techniques this assumption is fulfilled in theclinic). The linear actuator is now synchronized with the heartbeatdelayed by one full cardiac cycle in addition to the deadtime. Thisresults in a compensation of the cardiac disturbances. The heartbeat ofthe patient may be entered manually as an input to the control system orusing an automatic method of determining the cardiac frequency componentin the contact-force system. One such method includes pitch detection,which uses autocorrelation and peak detection to determine the cardiacfrequency. This value is then used to automatically update the value ofT.

For respiratory-motion-dominated targets in the heart, anothermodification to the Smith predictor may be introduced. Rather thanfurther delaying the feedback, a filter F(s) is introduced, as shown inFIG. 15D. F(s) takes the form of a low-pass filter designed to removehigh-frequency cardiac disturbances from the feedback pathway.

FIG. 15E shows a controller scheme that implements both cardiaccompensation (SP with θm) and respiratory compensation (SP with F(s))algorithms. The components shown within the boundaries of the dottedline are processed in real-time on a microcontroller. Switching betweenthe two control algorithms can be either manual or automatic. Forinstance, if the physician is manipulating a catheter to a target andnotices that the contact-force profile is dominated by cardiac motion,the cardiac compensation (SP with θm) will be enabled (switch down). Ifthe profile is dominated by respiratory motion, the respiratorycompensation (SP with F(s)) is enabled (switch up). Alternatively,frequency analysis of the force signal combined with peak detection canbe used to determine if the CF profile is dominated by cardiac orrespiratory motion and automatically select which algorithm to performfor the ablation. As a further alternative, a single controller, such asan Extended Kalman Filter (EKF), Model Predictive Controller (MPC) oranother predictive control algorithm, may be implemented tosimultaneously compensate for multiple disturbances, including bothcardiac and respiratory disturbances.

FIG. 16 shows a series of simulations using different configurations ofthe control schemes shown in FIG. 15. FIG. 16A shows the differencebetween PID and Smith predictor (SP). FIG. 16A shows a CF profile overtime. Initially the CFC is disabled and then engaged and programmed todeliver 20 g of force at the 30-second mark using PID. At the 60-secondmark the controller was switched to a SP. The PID gains were optimallychosen for the large deadtime in the system. Although the SP performedonly slightly better than the PID, the capability of adding modifiers tothe feedback path makes the SP a superior control system.

FIG. 16B is a simulation that shows a comparison between SP (as shown inFIG. 15B) and SP with a cardiac disturbance modifier (SP with θm; asshown in FIG. 15C). Similar to the simulation shown in FIG. 16A,initially the CFC is disabled and then engaged to deliver 20 g of forceat the 20-second mark using SP. At the 40-second mark, the modifier wasenabled. Since the CF profile is dominated by cardiac motion, the SPwith a cardiac disturbance modifier (SP with θm) is expected to performwell, which it does.

FIG. 16C is a simulation that shows a comparison between SP (as shown inFIG. 15B) and SP with a respiratory disturbance modifier (SP with F(s);as shown in FIG. 15D). Similar to the simulation shown in FIG. 16A,initially the CFC is disabled and then engaged to deliver 20 g of forceat the 50-second mark using SP. The F(s) modifier is added at the100-second mark. Since this CF profile is dominated with respiratorymotion, both SP and SP with F(s) are expected to work well. However, theF(s) filter does reduce the amount of CF variation in the output force.

FIG. 17 shows recorded CF profiles from experiments involving in vivocatheter contact at various target locations in a pig heart. For theseexperiments, a male farm pig was prepared for catheterization. The pigwas prepared with left and right femoral entry access points forcatheter insertion.

Target locations in the right atrium and left atrium were evaluated. Foreach location the catheter tip was manipulated to the target locationand manually maintained to provide 20 g of force for 30 seconds, whilethe contact force (CF) profile was recorded. Following this, the CFC wasengaged and programmed to deliver 20 g of force; the controlled CFprofile was recorded. To maintain consistency, the catheter tip was notrepositioned between manual and CFC-controlled profiles. Thecatheter-tissue incident angle was kept <30 degrees.

FIG. 17A shows results from an experiment performed in the left atriumof a pig. As the catheter comes in contact with the tissue, there arelarge force fluctuations due to the heart beating. When thecontroller—programmed to maintain 20 grams of force—is turned on (dashedline), these fluctuations drastically decrease and the contact-forcelevel is constant. During this time the linear actuator is moving thecatheter tip in synchrony with the heart and maintaining a desired levelof force.

FIG. 17B shows a recorded CF profile from another experiment in theright atrium. Once again, the controller is initially disabled and thenturned on (dashed line) to deliver a programmed force of 20 grams. Thedesired force is reduced to 10 grams at approximately 13.5 s thenreturns to 20 grams at 25 s demonstrating contact-force control.

The results shown in FIGS. 17A and 17B demonstrate that the cardiaccompensation algorithm performs extremely well when motion is dominatedby cardiac motion disturbances; which is often the case since for manyablation procedures the patient is subjected to apnea (temporarilyforcing the patient to hold their breath) during catheter ablation.However, there are cases where apnea cannot be utilized and respiratorymotion is dominant. In these areas the cardiac compensation algorithmdoes not compensate for respiratory motion disturbances adequately. FIG.17C shows a reduction of cardiac disturbances, but little to noreduction in respiratory motion disturbances. This is another experimentperformed in the left atrium of the pig.

FIG. 17D shows results from another experiment in a pig—the right atrialseptum is dominated by respiratory motion while cardiac motion isminimal. The cardiac compensation controller would be ineffective inremoving these low-frequency disturbances. The respiratory compensationcontroller was turned on (dashed line) for 20 grams of force, resultingin a significant improvement in response.

Several RF ablations were delivered in the left atrium and right atrium.Recorded CF profiles (not shown) confirm that a desired contact forcewas maintained during ablation delivery. Removal and inspection of thepig's heart provided visual confirmation (not shown) of ablationlesions.

Ideal control applications do not have significant deadtime in theirfeedback loop. Low deadtime enables high gain resulting in superiordisturbance rejection. In contrast, high deadtime inhibits the responseof the control and performs poorly. The integrator term in the PIDcontroller is particularly sensitive to deadtime in the control loop.The function of this term is to continue to ramp up the controller'soutput so long as there is an error between a desired CF and a measuredCF. Deadtime within the loop can reduce performance, may causeinstability, and may lead to poor disturbance rejection. The higher theamount of deadtime in the system, the less capable the PID will be toreject output disturbances.

While PID is sensitive to deadtime, PID can provide acceptable controlat lower levels of deadtime. A number of techniques are available todetermine suitability of PID in a system with deadtime. For example, oneapproach is to determine the time constant of the real-world processG(s) and compare the time constant to the deadtime. If the deadtime ofthe system exceeds the time constant of the system, time-delaycompensating algorithms such as a deadtime compensation or othermodel-based control techniques will typically perform better than PID(W. L. Wade, Basic and Advanced Regulatory Control: System Design andApplication, 2004, ch. 6, pp. 136). In practice, if the deadtime exceedsmore than two times the time constant a time-delay compensatingalgorithm such as a Smith predictor is often implemented.

For the implementation of the CFC device in the pig heart experimentsshown in FIG. 17, the process model Ĝ(s) can be modeled by either a 1st-or 2nd-order transfer function, with a time constant of 30 ms or 34 ms,respectively. For this same implementation, the observed deadtime of thesystem (about 100 ms) exceeds the time constants by a factor of three,and based on this observation, a time-delay compensating algorithm suchas the Smith predictor can offer benefit.

Another approach to determine whether PID is suitable to a particularimplementation with deadtime is to inspect CF profiles obtained fromsimulations or experiments for indications of instability or compromisedperformance. For example, FIG. 18 shows several CF profiles for animplementation with a PID controller comparing the effect of deadtime ona CF profile. FIG. 18A shows several plots that may be compared for astability analysis while FIG. 18B shows several plots that may becompared to analyze disturbance rejection.

FIG. 18A shows the step response of the process model Ĝ(s) using a PIDcontroller with increasing deadtime in the absence of any disturbance(eg., cardiac motion and respiratory motion disturbances are notpresent). These simulations show that when deadtime surpasses timeconstant (30 ms or 34 ms as described above), the controller becomesunstable. Note the significant ringing (overshoot) when deadtime is 34ms and the instability when deadtime is 40 ms. The deadtime in the pigexperiment implementation is more than 3 times larger than time constantof the process model, and therefore would benefit from a time-delaycompensating algorithm compared to a standard PID algorithm. Reducingthe gains of the PID controller may mitigate the stability problemevident at 40 ms of deadtime; however the controller would then besluggish with poor disturbance rejection.

FIG. 18B shows CF profiles that demonstrate rejection of outputdisturbances using a PID controller with varying deadtime. In each ofthe plots the disturbance is the same (note that the 45 ms and 50 msplots are on a different scale than the other four plots), which in thissimulation is modeled as a sine sweep from 0 to 2.5 Hz at 10 gpeak-peak, covering a representative range of frequencies found in theheart. The plots show that when deadtime is absent (0 ms), the output CFis well regulated and maintains a desired value. Correspondingsimulations with delays of 20 ms, 34 ms and 45 ms, respectively, in thefeedback loop also show that output CF can be maintained on a desiredvalue. In contrast, poor performance and instability is evident in the45 ms and 50 ms plots. The simulations show that the system becomesunstable with only 45 ms of delay (>time constant) with disturbances inthe frequency range of the heart (0.1 to 2.5 Hz). The amount of observeddeadtime (averaging approximately 100 ms) present in the system in thepig experiment implementation is more than twice of the 45 ms deadtimeshown in this simulation, indicating that a time-delay compensatingalgorithm would outperform a PID controller.

Calibration can be useful for accurately determining deadtime in asystem and improving modeling of modifiers to compensate for deadtime.Accordingly, the method of controlling the CFC device can include acalibration step. Similarly, the system may include a calibrator moduleor component. Sophisticated catheter mapping systems are hosted ongeneral-purpose operating systems, which process tasks with variousdegrees of complexity and priority. This may result in a deadtime thatis not consistent from procedure-to-procedure or day-to-day. Thus, acalibrator may be used prior to each procedure, or periodically asdesired. Although control systems are fairly robust, a calibration stepcan be advantageous in that it allows the deadtime θp to be estimatedaccurately to improve modeling of an estimated deadtime θpm.

In an example of a calibration step, a comparison is made between CFdata received from an external ideal force sensor (strain gauge) and CFdata received from a force sensor located at a remote end of a catheterthat is used during a medical procedure. The external ideal force sensor(strain gauge) comes in dynamic contact with the force-sensing catheter.The contact-force readings from both the strain gauge and the catheterforce sensor are simultaneously recorded. A cross-correlationcalculation between both contact-force data sets is used to model theestimated deadtime θpm in the system. A dedicated (separate) device canbe used to do this. This calibration step can also be used tomodify/correct Ĝ(s) if necessary (time constant and Ĝ(s) may varyslightly from catheter-to-catheter).

The CFC device may be used to adjust for any disturbance that may impactupon contact-force between a catheter tip and a target tissue.Disturbances of cardiac motion, respiratory motion, patient motion andcatheter instability are illustrative, and other disturbances may beaccommodated.

The CFC device may be used in combination with any force sensingcatheter and/or any robotic system incorporating a force sensingcatheter. The force sensing catheter and/or the robotic systemincorporating a force sensing catheter may support any number of degreesof freedom of motion of the catheter with any number of actuatorswithout limiting implementation of the CFC device. The CFC device can bean add-on tool compatible with commercially available, existingforce-sensing catheters and sheaths.

The CFC device, and systems and methods incorporating the same may beused for medical treatment. The CFC device, and systems and methodsincorporating the same may find use in any suitable catheter procedurefor any suitable target tissue. RF catheter ablation is an illustrativeexample, of catheter ablation and other types of catheter ablation maybe accommodated, including for example cryoablation. Ablation treatmentsincorporating the CFC device need not be limited to cardiac tissue, andmay accommodate other target tissues including, for example, liver.

The CFC device may be used in combination with an imaging systemproviding image data of a catheter tip and/or a target tissue. Anysuitable imaging system may be used including magnetic resonanceimaging, x-ray computed tomography or ultrasound.

The computer-implemented control of the CFC device typically requires amemory, an interface and a processor. The types and arrangements ofmemory, interface and processor may be varied according toimplementations. For example, the interface may include a softwareinterface that communicates with an end-user computing device. Theinterface may also include a physical electronic device configured toreceive requests or queries from an end-user.

Although a microprocessor or microcontroller was used in experimentsdescribed above, many other computer device types may be used includingfor example, a programmable logic controller or a field programmablelogic/gate array. Moreover, any conventional computer architecture maybe used for computer-implemented control of the CFC device including forexample a memory, a mass storage device, a processor (CPU), a Read-OnlyMemory (ROM), and a Random-Access Memory (RAM) generally connected to asystem bus of data-processing apparatus. Memory can be implemented as aROM, RAM, a combination thereof, or simply a general memory unit.Software modules in the form of routines and/or subroutines for carryingout features of the CFC device for maintaining a desired contact-forcecan be stored within memory and then retrieved and processed viaprocessor to perform a particular task or function. Similarly, one ormore compensation algorithms may be encoded as a program component,stored as executable instructions within memory and then retrieved andprocessed via a processor. A user input device, such as a keyboard,mouse, or another pointing device, can be connected to PCI (PeripheralComponent Interconnect) bus. The software will typically provide anenvironment that represents programs, files, options, and so forth bymeans of graphically displayed icons, menus, and dialog boxes on acomputer monitor screen.

A data-process apparatus can include CPU, ROM, and RAM, which are alsocoupled to a PCI (Peripheral Component Interconnect) local bus ofdata-processing apparatus through PCI Host Bridge. The PCI Host Bridgecan provide a low latency path through which processor may directlyaccess PCI devices mapped anywhere within bus memory and/or input/output(I/O) address spaces. PCI Host Bridge can also provide a high bandwidthpath for allowing PCI devices to directly access RAM.

A communications adapter, a small computer system interface (SCSI), andan expansion bus-bridge may also be attached to PCI local bus. Thecommunications adapter can be utilized for connecting data-processingapparatus to a network. SCSI can be utilized to control a high-speedSCSI disk drive. An expansion bus-bridge, such as a PCI-to-ISA busbridge, may be utilized for coupling ISA bus to PCI local bus. PCI localbus can be connected to a monitor, which functions as a display (e.g., avideo monitor) for displaying data and information for an operator andalso for interactively displaying a graphical user interface.

Computer-implemented control of the CFC device may accommodate any typeof end-user computing device including computing devices communicatingover a networked connection. The computing device may display graphicalinterface elements for performing the various functions of the systemsuch as selecting a pre-set desired contact force, selecting a controlalgorithm, selecting a compensation algorithm, modifying an existingcontact-force setting or an existing control algorithm or an existingcompensation algorithm, or updating a database of an activity log thatmay be locally stored in the computing device. For example, thecomputing device may be a desktop, laptop, notebook, tablet, personaldigital assistant (PDA), PDA phone or smartphone, gaming console,portable media player, and the like. The computing device may beimplemented using any appropriate combination of hardware and/orsoftware configured for wired and/or wireless communication.Communication can occur over a network, for example, where remotecontrol or remote monitoring of the CFC device is desired.

If a networked connection is desired the CFC device and its controllingsystem may accommodate any type of network. The network may be a singlenetwork or a combination of multiple networks. For example, the networkmay include the internet and/or one or more intranets, landlinenetworks, wireless networks, and/or other appropriate types ofcommunication networks. In another example, the network may comprise awireless telecommunications network (e.g., cellular phone network)adapted to communicate with other communication networks, such as theInternet. For example, the network may comprise a computer network thatmakes use of a TCP/IP protocol (including protocols based on TCP/IPprotocol, such as HTTP, HTTPS or FTP).

The CFC device and systems incorporating the same as described hereinand each variant, modification or combination thereof may be controlledby a suitable computer-implemented method. A method of controlling theCFC device includes detecting contact force data with a force sensorlocated at a remote end of a catheter; receiving the contact force datawith a controller; and generating and communicating a control signal tothe linear actuator to minimize a difference between the real-timecontact force data and a preset desired contact force. For example, asdescribed with reference to control algorithms schematically representedin FIG. 15, the method includes calculating an error between themeasured output CF and the desired CF; inputting the error into thecontroller C(s), where an appropriate control signal is calculated; andcommunicating the control signal to the linear actuator of the motorwith the motor response providing catheter tip movement and subsequentmeasurement and communication of a CF value to reinitiate and repeat theloop (the dynamics of this system, including deadtime Op, are capturedin G(s)). Where a deadtime of sufficient magnitude is present the methodmay optionally include generating a delay-based modifier modeled on anidentified time delay; and applying the delay-based modifier to thecontrol signal. The identified time delay may be determined byidentifying a time delay between the steps of detecting the contactforce data and receiving the contact force data. Again with reference toFIG. 15 for example, these optional method steps for deadtimecompensation include inputting the control signal to a numerical modelĜ(s) that outputs a delay-based modifier that is an estimate of the CFvalue without deadtime which is then delayed by θpm, an estimate of theprocess delay θp which results in a further delay-based modifier that issubtracted from the measured output CF; and then the CF value withoutdelay is added. Further optional method steps may include applying acardiac modifier to the control signal to compensate for cardiac motiondisturbances with the cardiac modifier optionally generated by measuringa heart rate and deriving the cardiac modifier based on the heart rate.Again with reference to FIG. 15, the step of applying the cardiacmodifier is illustratively shown as further delaying the estimate of theCF value without deadtime combined with bpm by adding θm whose purposeis to synchronize the linear actuator with the heart rate. Furtheroptional method steps may include applying a respiratory modifier to thecontrol signal to compensate for respiratory motion disturbances; therespiratory modifier can be a low-pass filter set to remove highfrequency disturbances present in the contact force data. Furtheroptional method steps may include receiving real-time patient specificdata with the controller and using the real-time patient specific datato generate the control signal to minimize the difference between thereal-time contact force data and the preset desired contact force; thereal-time patient specific data may be tissue temperature at a contactpoint with the catheter, electrocardiogram, respiratory rate,catheter-tissue incident angle, or any combination thereof. A furtheroptional method step may include displaying the contact force data on acomputer monitor. A further optional method step may include receivingreal-time imaging data of the remote end of the catheter and displayingthe imaging data on the computer monitor. A further optional method stepmay include calculating a force-time integral (FTI), and automaticallysending a control signal to retract the catheter once a preset desiredFTI is reached.

The CFC device and systems incorporating the same as described hereinand each variant, modification or combination thereof may also beimplemented as a method or computer programmable/readable code on anon-transitory computer readable medium (i.e. a substrate). The computerreadable medium is a data storage device that can store data, which canthereafter, be read by a computer system. Examples of a computerreadable medium include read-only memory, random-access memory, CD-ROMs,magnetic tape, SD card, optical data storage devices and the like. Thecomputer readable medium may be geographically localized or may bedistributed over a network coupled computer system so that the computerreadable code is stored and executed in a distributed fashion.

Embodiments described herein are intended for illustrative purposeswithout any intended loss of generality. Still further variants,modifications and combinations thereof are contemplated and will berecognized by the person of skill in the art. Accordingly, the foregoingdetailed description is not intended to limit scope, applicability, orconfiguration of claimed subject matter.

What is claimed is:
 1. A catheter force control system comprising: ahand-held catheter force control device comprising: a base sized to behand-held; a cover reversibly fastened to the base in a closed position;a sheath clamp coupled to the base, the sheath clamp capturing a sheathhandle of a sheath to immobilize the sheath handle relative to the base,the sheath clamp is an aperture formed in corresponding abutting edgesof the cover and the base, the aperture being formed when the cover andthe base are in the closed position; a catheter clamp capturing acatheter, a remote end of the catheter configured to deliver an ablationtherapy; the catheter clamp aligned to be substantially co-axial withthe sheath clamp; and a linear actuator effecting linear motion of thecatheter clamp relative to the sheath clamp; a force sensor located atthe remote end of the catheter, the remote end configured for contactwith a target tissue, the force sensor detecting real-time contact forcedata; a controller for receiving the real-time contact force data, andfor generating and communicating a control signal to the linear actuatorto minimize a difference between the real-time contact force data and apreset desired contact force during ablation therapy delivery to thetarget tissue, the control signal adjusting a position of the linearactuator to compensate for a contact disturbance of the remote endconfigured for contact with the target tissue.
 2. The system of claim 1,wherein the controller is a proportional-derivative-integral (PID)controller, a hybrid PID controller, a Smith predictor controller, aKalman filter controller or any combination thereof.
 3. The system ofclaim 1, wherein the controller includes a delay-based modifier tocompensate for a delay in receiving the real-time contact force datawithin the system, a cardiac modifier to compensate for cardiac motiondisturbances, or a respiratory modifier to compensate for respiratorymotion disturbances.
 4. The system of claim 1, wherein the controllerreceives real-time patient specific data and uses the real-time patientspecific data to generate the control signal to minimize the differencebetween the real-time contact force data and the preset desired contactforce.
 5. The system of claim 4, wherein the real-time patient specificdata is tissue temperature at a contact point with the catheter,electrocardiogram, respiratory rate, catheter-tissue incident angle, orany combination thereof.
 6. The system of claim 1, further compromisinga foot pedal for controlling a start of the system, a stop of thesystem, or both the start and the stop of the system.
 7. The system ofclaim 1, further comprising a robotic catheter navigation modulecommunicative with the hand-held catheter force control device toadvance the catheter through the sheath to the target location.
 8. Thesystem of claim 1, wherein the catheter delivers a desired Force-TimeIntegral (FTI).
 9. The system of claim 8, wherein the controller isprogrammed to calculate the FTI, and automatically sends the controlsignal to retract the catheter once the desired FTI is reached.
 10. Amethod of controlling force of a catheter configured for contact with atarget tissue, the method comprising: coupling a catheter and a sheathto a hand-held catheter force control device, the device comprising: abase sized to be hand-held; a cover reversibly fastened to the base in aclosed position; a sheath clamp coupled to the base, the sheath clampcapturing a sheath handle of the sheath to immobilize the sheath handlerelative to the base, the sheath clamp is an aperture formed incorresponding abutting edges of the cover and the base, the aperturebeing formed when the cover and the base are in the closed position; acatheter clamp capturing the catheter, a remote end of the catheterconfigured to deliver an ablation therapy; the catheter clamp aligned tobe substantially co-axial with the sheath clamp; and a linear actuatoreffecting linear motion of the catheter clamp relative to the sheathclamp; detecting real-time contact force data with a force sensorlocated at the remote end of the catheter, the remote end configured forcontact with a target tissue; receiving the real-time contact force datawith a controller; and generating and communicating a control signalfrom the controller to the linear actuator to minimize a differencebetween the real-time contact force data and a preset desired contactforce during ablation therapy delivery to the target tissue, the controlsignal adjusting a position of the linear actuator to compensate for acontact disturbance of the remote end configured for contact with thetarget tissue.
 11. The method of claim 10, further comprising:generating a delay-based modifier modeled on an identified time delay;and applying the delay-based modifier to the control signal.
 12. Themethod of claim 11, wherein the identified time delay is determined byidentifying a time delay between detecting the real-time contact forcedata and receiving the real-time contact force data.
 13. The method ofclaim 11, wherein the delay-based modifier is generated by a Smithpredictor algorithm.
 14. The method of claim 11, wherein the delay-basedmodifier is generated by a Kalman filter algorithm.
 15. The method ofclaim 11, further comprising applying a cardiac modifier to the controlsignal to compensate for cardiac motion disturbances.
 16. The method ofclaim 11, further comprising applying a respiratory modifier to thecontrol signal to compensate for respiratory motion disturbances. 17.The method of claim 10, further comprising receiving real-time patientspecific data with the controller and using the real-time patientspecific data to generate the control signal to minimize the differencebetween the real-time contact force data and the preset desired contactforce.
 18. The method of claim 17, wherein the real-time patientspecific data is tissue temperature at a contact point with thecatheter, electrocardiogram, respiratory rate, catheter-tissue incidentangle, or any combination thereof.
 19. The method of claim 10, furthercomprising calculating a force-time integral (FTI), and automaticallysending the control signal to retract the catheter once a preset desiredFTI is reached.
 20. A method of delivering ablation therapy to a subjectin need thereof comprising delivery of an ablation to a target locationin the subject using the catheter coupled to the system of claim 1.